StickyShisha, are those the LW 6-arms? I've got one of them, 18/14 though, and its great.
appa juice: if you find a piece that you like at a good price (like the RXI photobooth posted perhaps) that's outfitted for a 14mm connection, it might be worth it to just grab one of
these for such a reasonable price. Obviously its worth it to look around for that 18mm nonetheless though, RXI might even be willing to swap one out for you?
EDIT: Stu beat me to it with a good idea. H20 adaptor or 14mm/18mm enlarger are both cheap options either way.